Allelic polymorphism of two multifunctional regions in the central human MHC: tenascin X, XB-S and YB, and their duplicated fragments XA and YA.

Abstract

Two highly polymorphic sequences have been discovered in the complement C4 region of the human major histocompatibility complex (MHC). They are part of a duplicated unit of overlapping genes, transcribed in opposite directions and containing the sequences of tenascin X (XB), XB-S, XA, YB and YA. Fragments of 1014 bp and 894 bp were co-amplified by polymerase chain reaction (PCR) and digested with two different restriction enzymes. This preliminary study provides evidence for more than five different alleles each of XA (YA) and XB (XB-S, YB), and at least 11 XA-XB haplotypes. Their association with extended HLA-B-DR haplotypes, C4 complotypes, and C4 region restriction fragment length polymorphisms (RFLP) is discussed. X gene polymorphisms are a complement region marker system that should be uniquely suited for PCR-based typing methods. They could become a useful addition to HLA class I and class II markers in the mapping of candidate genes for MHC-associated diseases, including the X and Y genes themselves.